Thermal insulation — density, strength and fire class are one decision.
XPS, EPS, rock wool, PIR and faced systems for walls, roofs and floors. The awkward thing about this category: a board can meet the thermal target, miss the compressive strength, and still carry a certificate that looks complete. The three properties are traded against each other, and the trade is where the money is.
What we buy
- XPS boards — extruded polystyrene for floors, basements, inverted roofs and cold storage, specified by compressive strength rather than thickness alone.
- EPS boards — moulded and graphited grades, for external wall systems and cavity fill.
- Rock wool — boards, batts and lamella for fire-rated walls, rainscreen cavities and acoustic applications.
- PIR and PUR boards — foil-faced rigid foam for tight build-ups where thickness is the constraint.
- Faced and laminated systems — foil, glass tissue, cement and plasterboard facings, and insulated sandwich panels.
- Accessories — anchors and fixings, mesh, renders, adhesives, tapes, vapour barriers and membranes.
The thing that actually goes wrong
The board arrives with the right thickness and the right declared lambda. It also has a density below what the specification assumed, which means the compressive strength is not there and the render system above it will crack at the board joints within a heating season.
Or the fire class is quoted from a test on the uncoated core, while what you bought is a faced product whose face changes the reaction-to-fire result. Both are paper-legal. In insulation, the properties are a package — buying one of them is how you end up with none of them.
How we handle it
Before quoting we write down the four numbers that matter for your assembly: the thermal resistance required, the compressive strength at the relevant deformation, the reaction-to-fire class required by the application, and the water absorption or dimensional stability limit for the exposure. Any factory can hit one of these. The quote is only useful if it states all four.
We ask for the factory's own production test records, not only the type-test certificate. Density and compressive strength are measured per batch at the plant; if the plant cannot show a batch record, the certificate is a description of a product they once made. Where the application is critical, we send a sample from the production batch to an independent lab.
At loading we check the board marking, the density stated on the pallet label, and the facing against the approved sample. Insulation is rarely visibly wrong, which is exactly why the numbers on the label have to be checked rather than trusted.
Questions specific to this line
Is freight a problem for insulation?
+It is the dominant cost, and it decides whether the line makes sense at all. Insulation is mostly air, so you are paying to ship volume. That is why insulation is usually a full-container purchase and why the compression ratio of the board matters — some grades pack tighter than others. We will model the landed cost per square metre before recommending anything, and sometimes the answer is that local supply wins.
How do we verify density, since that is where the substitution happens?
+Two ways that actually work. First, ask for the plant's batch test records and compare the density and compressive strength figures across several batches — a factory that measures will have the numbers, one that doesn't will send the type test again. Second, weigh a measured volume of board from the production batch. Density is mass over volume; a scale and a tape measure catch most of it, and an independent lab settles the rest.
Does the fire class transfer across markets?
+Not automatically. EN 13501 and GB 8624 are different classification systems with different test methods, and a Chinese B1 does not map cleanly onto a European B-s1,d0. If your building permit depends on a specific class, that class has to come from a test to the standard your authority recognises — on the finished product, with the facing, not on the core alone. We will tell you which of those the factory can actually produce.
Can you supply the whole system, not just the board?
+Yes, and for external wall systems that is usually the right way to buy it. Board, adhesive, mesh, render, anchors and trims from one source means one party is responsible for compatibility — which is where these systems fail when they fail. It also means the fire test, if there is one, covers the system rather than the components.